A buffer circuit (sometimes simply called a buffer) is one that provides electrical impedance transformation from one circuit to another. Buffer circuits are frequently used for intermediate frequency (IF) buffers in receiver devices having parallel channels. Buffers are often used as output stages (i.e. output buffers) on the receiver channels. Depending on application requirements, and considering that parallel channels are used in such receiver devices, one channel may be selected to be active, while the other is powered down. In these output buffers normally bipolar transistors are used because of their superior performance in terms of large output voltage swings, low supply currents, good linearity, and good current drive capability (size) as compared MOS devices.
In those applications, each IF buffer may comprise an emitter follower having an emitter of a bipolar transistor as an output. To save costs and space, often AC-coupling capacitors are left out, and so the emitters of the different bipolar transistors are directly connected. As a result, the bipolar transistor of the unused output stage may leave its safe operation region when a switch-off is implemented pulling its base to ground. In that situation, the emitter voltage of the bipolar transistor of the switched-off buffer may even get to a level that a base-emitter-voltage of that bipolar transistor exceeds the reverse breakdown limit, which results in unwanted breakdowns. This will degrade the performance and will limit the life time of the circuit.